Sugar Sprays to Encourage Beneficial Insects

Can spraying sucrose (table sugar) solutions on plants increase populations of natural enemies? Two recent studies one in Honduras on corn and another in Colorado on alfalfa showed increased numbers of predators in these crops with sugar sprays. There are also several commercially available food spray supplements designed to increase predators and parasites. Some of these are primarily sugar; others are based on yeast, and contain more protein.

Evaluate your own applications of sugar sprays, or commercial food spray supplement(s), by counting predatory insects (lady beetles and green lacewings), as well as monitoring pest levels in the different treatments being compared. Plot size can vary, but make sure they are large enough (or separated by untreated areas) to minimize insect movement. Make enough sugar solution to treat half of the plots. Use a rate of 14-20 pounds of sugar dissolved in 10-20 gallons of water per acre, or for smaller areas, use 150 g (1/3 pound) sugar in a liter of water. Spray half of the plots with the sugar solution, the other half with plain water. In corn, sprays should probably be applied relatively early (in whorl stage) to allow enough time for beneficial insects to build up before pest populations increase.

Count the number of predators on 10 plants per plot just before treatment and continue at weekly intervals after spraying. Yellow sticky traps can also be used to measure levels of lady beetles and lacewings. Use extension recommended practices to monitor the important pest species in your area. In which plots did you find the most predators? Did they seem to have any effect on pest populations in those plots?

- Bob Wright, University of Nebraska

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